At the start, Facebook Home is available only to Android users in the United States and only to those who are using a HTC First, HTC One X, HTC One X+, Samsung Galaxy S III and the Samsung Galaxy Note II.

It also will be available for Samsung Galaxy S4 and HTC One users when those phones are released, according to a Facebook spokeswoman.

Facebook Home, the social network's new launcher for Android phones, is live and ready for download today from Google Play.

Facebook Home, which doesn't replace the Android OS but sits on top of it, includes a family of Facebook-focused apps and also works with the apps a user already has on her phone.

Users with compatible phones should update their Facebook apps and then go to Google Play and search for "Facebook Home." After the install, users will be asked to pick a launcher.

Once it's installed, they'll experience their smartphone through a Facebook lens.

With Home, the first thing a user sees when she fires up her phone is a feature called Cover Feed, which replaces the phone's usual lock screen. The new feature gives the user information about what her friends are doing, a family birthday party or her favorite sports team's big win, bringing her directly into her social network from the start.

The new launcher also includes Chat Heads, a new app that lets a user chat with friends even while he's doing other things in his phone. For instance, he might be listening to music or writing an email, when his friend's face will pop up on the screen if she's trying to reach him.

Home is a big advance in the mobile market for a company that just last spring listed mobility among its biggest "risk factors" in an amended filing with the U.S. Securities and Exchange Commission, The company admitted that the quickening shift from traditional desktop or laptop computers to mobile devices was hurting Facebook's advertising plan, since it had no way to monetize this growing mobile trend.

Facebook has been making inroads, though, having acquired Instagram, a popular photo-sharing app, last year, redesigned its iOS app and delivered new development tools for iOS and Android.